Respiratory Physiology

Question 1

Describe the functions of the respiratory system

Answer 1

• Provides O2 to the blood
• Removes CO2 from the blood
• Regulates [H+] (blood pH)
• Speech
• Microbial defense
• Influences arterial [] of chemical messengers
• Traps and dissolves small blood clots

Question 2

Describe the anatomy of the lungs.

Answer 2

• Suspended in thoracic cavity
  
  • thoracic cavity separated from abdominal cavity by diaphragm (skeletal muscle)
• Surrounded by chest wall
• Space b/w lung & chest wall = intrapleural space

Question 3

Differentiate between 2 major divisions of the lungs:

• Conducting zone
• Respiratory zone

Answer 3

Conducting zone:

• Air travels through and is conditioned to be safe for gas exchange. Includes…
  
  • humidification
  • filtration
  • temperature change

Respiratory Zone:

• where the actual gas exchange occurs

Note: Bronchioles exist in both zones:

• Terminal Bronchioles (conducting zone)
• Respiratory Bronchioles (respiratory zone)

Question 4

Describe the blood vessels and the blood flow in the pulmonary artery.

Answer 4

• Pulmonary artery branches extensively
• Forms a dense network of capillaries
• Capillaries wrap around alveoli
• To maxmize diffusion of gases, the blood is exposed to the largest SA and lowest velocity of blood flow in the capillaries
  
  • Gas exchange thakes place in the alveoli at the blood-gas barrier (BGB)
    
    • BGB separates blood in pulmonary capillaries from air in alveoli
    • Air to one side of barrier by ventilation;
    • Blood to other side through pulmonary circulation

Question 5

What is…

• Pulmonary ventilation (V_E)
• Alveolar ventilation (V_A)
• Anatomical dead-space ventilation (V_D)

What is the equation used to calculate each?

Answer 5

Pulmonary ventilation (V_E):

• volume of air entering the entire lung (both conducting & respiratory zones) in one minute
• V_E = tidal volume x respiratory rate

Alveolar ventilation (V_A):

• volume of air entering only the respiratory zone in one minute
• represents volume of fresh air available for gas exchange

Anatomical dead-space ventilation (V_D):

• volume of air found in the conducting zone
  (not involved in gas exchange)
• measured in mL for a normal person in upright position = ~body weight in pounds
  i.e. body weight of 100lbs = dead space volume of 100mL

To calculate V_A:
V_A = V_E - V_D

Note:
Tidal volume - volume in one breath

Respiratory rate - # of breaths per minute

Question 6

Calculate V_A given:

• Body weight 150 lb
• Respiratory Rate: 10 breaths/min.
• Tidal Volume: 600 mL/breath
• V_E: 6000 mL/min

Answer 6

V_A = V_E - V_D

• Tidal Volume of 600mL inhaled
• ~ 150 mL remains in conducting zone (no alveoli)
  
  • 600mL - 150mL = 450 mL
• Remainder 450 mL reaches the respiratory zone (alveoli present) and participates in gas exchange
  
  • 450mL x 10 breathes/min = 4500 mL/min

​OR,

= V_E - (Dead space x RR)
= 6000 - (150 x 10)
= 4500

Question 7

What does Boyle’s Law state and how does it apply to respiratory physiology?

Answer 7

Boyle’s Law:

• For closed volume of gas (at constant temperature), pressure is inversely proportional to volume
  
  • Pressure ∝ 1/volume
  • when volume decreases, pressure increases v.v.

Application to respiratory physiology:
Changes in the volume of thoracic cavity results from the action of respiratory muscles:

• Inflation of lung during inspiration & deflation of lung during expiration are brought by changing the volume of the thoracic cavity

Question 8

Describe the process involved in inspiration and expiration at rest and during exercise.

Answer 8

Inspiration:

• Diaphragm & external intercostals contract
• Bigger pleural cavity

Expiration:

• Diaphragm & external intercostals relax
• Smaller pleural cavity
• During exercise:
  
  • internal intercostals, obliques and rectus abdominus contract

Question 9

What is transpulmonary pressure and how is it calculated?

Answer 9

Transpulmonary pressure:

• Pressure generated due to the elastic recoil forces of both lungs and chest wall
• During inhalation:
  lungs slide against the chest wall
• After exhalation:
  ​lungs have the tendency to pull inwardly away from the chest wall
  
  • Lungs pull inwardly away from the chest ⇔ Chest wall pulls the chest wall outward
• To calculate:
  Transpulmonary pressure = difference b/w intrapulmonary pressure and intrapleural pressure

Question 10

What happens during a pneumothorax?

Answer 10

Pneumothorax is a collapsed lung. When air enters the fluid-filled intrapleural space, the build-up of air puts pressure on the lung so it cannot expand as much as it normally does when taking a breath, causing shortness of breath and chest pain.

Question 11

What is lung compliance?

Answer 11

Compliance is a measure of “stretchability” of the lungs

• more compliant the lung, easier it will stretch, increasing in volume during inhalation

Compliance =
change in lung volume/change in lung pressure

Question 12

What are the 2 factors that influence lung compliance?

Answer 12

Factors:

1. Elastic tissue components of the lung itself (~1/3)

• fibers of elastin (elastic lung tissue) and collagen present in alveolar walls throughout the lung
  
  • ​Fibers start in submucosal airways and become more and more distinct as they get closer to alveoli
  • 2 major competing models on how Elastin works:
    
    • ​Pierce and Ebert: Elastin and collagen are intertwined and encircle alveoli in a coiled fashion. When expanding, they “fold out” to let tissue expand.
    • Setnikar-Mead model: Collagen and elastin operate in parallel. At low volume, elastin stretches and collagen is loose. At high volume, collagen becomes taut and prevents elastin from snapping.

2. Surface tension inside alveoli (~2/3)

• Surface Tension: Force developed at the surface of a liquid due to the attraction b/w water molecules
  (think of putting drops of water on glass and putting another glass on top and trying to pull the two glass apart)
• Lungs have thin film of liquid that lines the inside of the alveoli; inside the intrapleural space. Due to this surface tension, the lungs and the chest wall have an elastic recoil force:
  
  • ​Lungs have the tendency to pull inwards
  • Chest wall have the tendency to pull outwards
• Due to this surface tension, the lungs always holds a residual volume of air, which is why the lung doesn’t collapse upon exhalation.

Question 13

To prevent alveolar collapse, surfactant is used. What is it, and what occurs as a result of a deficiency of surfactant?

Answer 13

Properties of pulmonary surfactant:

• reduces surface tension
  (prevents alveolar collapse)
• Microbial defense

Deficiency of surfactant leads to…

• Neonatal Respiratory Distress Syndrome (nRDS)
  
  • ​occurs in premature infants
    
    • poor lung function
    • alveolar collapse
    • hypoxemia
  • Lack mature surfactant system
  • To treat: administer surfactant

Question 14

Spirometers help measure lung volumes as well as help diagnose some respiratory diseases. Define the following lung volumes:

• Tidal volume
• Inspiratory Reserve Volume
• Expiratory Reserve Volume
• Residual Volume
• Total Lung Capacity
• Inspiratory Capcity
• Expiratory Capacity

Answer 14

Tidal Volume

• Volume of inhalation and exhalation during normal breathing

Inspiratory Reserve Volume

• Difference between maximum lung volume and resting inhalation volume

Expiratory Reserve Volume

• Difference between minimum lung volume and resting exhalation volume

Residual Volume

• Volume that we are incapable of exhaling

Total Lung Capacity

• The total volume of air in your lungs

Vital Capacity (aka Force Vital Capacity)

• The total volume of air that you can move in and out of your lungs on maximum inhalation/exhalation

Inspiratory Capacity

• Total volume of maximum inhalation starting from resting exhalation

Expiratory Capacity (aka Expiratory Reserve Volume)

• Total volume of maximum exhalation starting from resting exhalation

Question 15

FVC and FEV-1 are used to diagnose obstructive and restrictive diseases. What are they are how are they calculated?

Answer 15

Forced Vital Capacity (aka Vital Capacity)

Forced Expiratory Volume (in one second) (FEV-1):
– Maximum volume of air that can be exhaled in one second

FEV/FVC
= percentage of total breath that can be exhaled in one second

Question 16

Distinguish between obstructive and restrictive diseases and give examples of both.

Answer 16

Obstructive Disease

– FEV/FVC < 70% (80 according to class)

– Reduction in the speed at which air can move out of the lungs

• asthma: airway spasms in smooth muscle triggered by exercise, air pollution, allergies, cold air, viral…etc.
  
  • airway inflammation
  • airway hyperresponsiveness
    =airway narrowing
• chronic bronchitis: excessive mucus & inflammation in airways (smoking=chief cause!)
  
  • airway inflammation
  • enlarged mucus glands
  • excessive mucus in airways
• emphysema: walls between alveoli brea down, creating large air sacs (decreasing SA)
  (smoking=chief cause again!)
  
  • destruction of alveolar walls
  • loss of elastin
  • reduces elastic recoil

Restrictive Disease
– FEV/FVC > 85% (80 according to class)
– Reduction in amount of air that can be held in lungs

• pulmonary fibrosis: less compliant lung (stiff) due to fibrous scar tissue that forms in the alveoli and other lung tissue
  (increases collagen (ineasticity) in alveolar walls)
  
  • caused by…
    
    • chronic inhalation of asbetos
    • coal dust
    • pollution

Question 17

• Define partial pressure
• What is the atomspheric pressure and what is the atmosphere made up of?
• State the formula for calculating the partial pressure of a gas.
• Calculate PO₂ and PCO₂ of air at sea level

Answer 17

Partial pressure of a gas is the pressure exerted by a single gas in a mixture of gases while dissolved in a liquid.

Air at sea level exerts an atmospheric pressure of 760mmHg and is roughly made up of…

• 20.93% Oxygen
• 78 % Nitrogen
• 0.03% carbon dioxide, and other inert gases

Partial pressure =
total pressure of all gases x fractional [] of one gas

Ex. PO₂ = 760 mmHg x (20.93/100) = 159 mmHg
Ex. PCO₂ = 760 mmHg x (0.03/100) = 0.228 mmHg

Question 18

Circle the correct answer:

Gases must move down a pressure gradient. For oxygen to enter blood, it must have a higher/lower pressure in the alveoli, and a higher/lower pressure in the capillaries. Gas exchange occurs at the capillaries and cells of tissues.

What does Fick’s Law state?

List the 5 factors to maximize diffusion across BGB.

Answer 18

Gases must move down a pressure gradient. For oxygen to enter blood, it must have a higher pressure in the alveoli, and a lower pressure in the capillaries. Gas exchange occurs at the capillaries and cells of tissues.

Fick’s Law states…
Rate of diffusion= (gradient x SA) / thickness

5 factors:

• Thin membrane
• High SA
• High pressure gradient
• Slower blood velocity
• Lipid solubility

Question 19

Draw a diagram that shows the partial pressures of O₂ and CO₂ in the lungs and throughout circulation when the body is at rest.

Answer 19

Question 20

Describe the effects of changing ventilation on arterial PO₂, PCO₂ and pH:

• Holding breath without changing metabolic activity
• Hyperventilating without changing metabolic activity
• Increasing metabolic activity without changing ventilation

Answer 20

Holding breath without changing metabolic activity:

• Decreased PO₂
• Increased PCO₂
• Increased H⁺

Hyperventilating without changing metabolic activity:

• Increased PO₂
• Decreased PCO₂
• Decreased H⁺

Increasing metabolic activity without changing ventilation:

• Decreased PO₂
• Increased PCO₂
• Increased H⁺

Question 21

Name 6 components of blood:

Answer 21

6 components of blood:

• Red blood cells (RBCs; aka erythrocytes)
• White blood cells (WBCs; aka leukocytes)
• platelets
• plasma
• protein
• ions

Question 22

Describe 2 ways in which oxygen is transported in the blood.

Answer 22

1. Dissolved form in plasma
   (1. 5%):

• Normal blood with an arterial PO₂ of 100 mmHg contains only 3mL O₂/L blood.
  
  • Total blood volume of average individual is 5L, meaning only 15 mL of oxygen is carried in plasma
• Very inadequate bc even at rest, body consumes total of 250 mL O₂/min, requiring a cardiac output of 90 mL/min to survive

2. Bound to oxyhemoglobin insisde RBCs (HbO₂) (98.5%)

• Through combination with hemoglobin (Hb):
  
  • ​Hb is a protein complex found inside RBCs
    
    • ​2 alpha chains, 2 beta chains -
      each has a heme group that carries oxygen
    • Maximumof 4 oxygen carried per Hb (depending on [] of O₂ surrounding Hb)
  • O₂ easily forms a reversible combination with Hb to give oxyhemoglobin.
  • O₂ + Hb ⇔ HbO₂

Question 23

What are the 4 necessary functions of Hb?

Answer 23

1. Bind lots of O₂ at the lungs
2. Be able to dissociate O₂ at the cells of the body’s tissues for use
3. Pick up waste products (CO₂) from the cells
4. Bring CO₂ back to the lungs for disposal

Question 24

O2 + Hb ⇔ HbO2
What causes the direction of this equation?
Explain the concept using a hemoglobin dissociation curve and the Bohr Effect.

Answer 24

[PO₂]:

• Hb will have different amount of O₂ attached to it depending on the [] of O₂ surrounding Hb
  
  • ​Lower PO₂ results in less O₂ on Hb
• When saturation occurs, Hb is “full”

Bohr Effect: In the presence of CO₂ or H⁺, Hb has a decreased affinity for O₂:

• pH decreases:
  
  • Lower pH = more H⁺ (more acidic blood)
• CO₂ increases
• Temperature increases

CO₂ + H₂O ⇔ H₂CO₃ ⇔ HCO₃^- H⁺

​i.e. from exercise (aerobic respiration):
​When CO₂ is released from cells of body tissues into blood, it is converted into carbonic acid by carbonic anhydrase then is quickly converted into bicarbonate molecules and protons

Question 25

What are 3 ways in which carbon dioxide is carried in the blood?

Answer 25

1. Dissolved form (10%):
   * 10% of CO₂entering lungs are dissolved in plasma; CO₂ x20 more soluable than O₂
2. Carbamino form attached to blood protein (20%):
   * 20% of CO₂ diffusing into lungs are in carbamino Hb form
3. Bicarbonate form (70%):
   * 70% of CO₂ diffusing into lungs comes from HCO₃^-

Question 26

Describe chloride shift.

Answer 26

IN THE ALVEOLUS:

• Must shuttle Cl^- out of cell so reaction proceeds backwards
• Bicarbonate transported into cell
• Bicarbonate transformed into CO₂
• CO₂ exhaled

The opposite happens in the TISSUES:

• Cl^- shuttled in, bicarbonate out

Question 27

What is erythropoiesis and erythropoietin (EPO)?

Answer 27

• Takes place in bone marrow to produce RBCs
  
  • ~2M RBCs are produced (and die) ever sec!
• Control and regulate erythropoiesis, need hormone erythropoietin (EPO)
  
  • primarily from kidneys
• EPO stimulates bone marrow to produce RBCs
  
  • When oxygen levels in the kidney drop, EPO secretion increases

Question 28

Cause of drop in O₂ levels in the kidneys:

Answer 28

• Decrease in # of RBCs
  (less carrying capacity)
• Decrease in cardiac output
  (less blodd flow = less O₂)
• Lung disease
  (poor gas exchange i.e. emphysema)
• High altitude
  (lower atmospheric pressure)

Question 29

How is homeostasis achieved through ventilation patterns?

Answer 29

• NS adjusts pulmonary & alveolar ventilation to match O₂ demands & CO₂ production
  
  • esp. during strenuous exercise/other stress
• Through Negative Feedback!

Question 30

What are chemoreceptors?

• Define
• Types
  
  • Control of ventilation

Answer 30

Chemoreceptors are special receptors that respond to changes (i.e. PO₂, PCO₂, [H⁺]) in the chemical composition of blood/other fluid around the receptors.

Two sets of chemoreceptors in the body:
1. Central chemoreceptors (in the medulla)

• See image attached
  2. Peripheral chemoreceptors (in aortic arch & carotid body)
• see image (card #30)